Re: [PATCH 1/2] ALSA: pcm: Fix snd_pcm_hw_params struct copy in compat mode

[Takashi Iwai]

On Mon, 18 Jan 2016 14:35:00 +0100,
Nicolas Boichat wrote:
> 
> This reverts one hunk of
> commit ef44a1ec6eee ("ALSA: sound/core: use memdup_user()"), which
> replaced a number of kmalloc followed by memcpy with memdup calls.
> 
> In this case, we are copying from a struct snd_pcm_hw_params32 to
> a struct snd_pcm_hw_params, but the latter is 4 bytes longer than
> the 32-bit version, so we need to separate kmalloc and copy calls.
> 
> This actually leads to an out-of-bounds memory access later on
> in sound/soc/soc-pcm.c:soc_pcm_hw_params() (detected using KASan).
> 
> Signed-off-by: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>

Applied both patches with Cc to stable.  Thanks.


Takashi

> ---
>  sound/core/pcm_compat.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/sound/core/pcm_compat.c b/sound/core/pcm_compat.c
> index b48b434..9630e9f 100644
> --- a/sound/core/pcm_compat.c
> +++ b/sound/core/pcm_compat.c
> @@ -255,10 +255,15 @@ static int snd_pcm_ioctl_hw_params_compat(struct snd_pcm_substream *substream,
>  	if (! (runtime = substream->runtime))
>  		return -ENOTTY;
>  
> -	/* only fifo_size is different, so just copy all */
> -	data = memdup_user(data32, sizeof(*data32));
> -	if (IS_ERR(data))
> -		return PTR_ERR(data);
> +	data = kmalloc(sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	/* only fifo_size (RO from userspace) is different, so just copy all */
> +	if (copy_from_user(data, data32, sizeof(*data32))) {
> +		err = -EFAULT;
> +		goto error;
> +	}
>  
>  	if (refine)
>  		err = snd_pcm_hw_refine(substream, data);
> -- 
> 2.6.0.rc2.230.g3dd15c0
> 
>